Work vehicles, such as conventional loaders are normally provided with a bucket carrying boom structure that moves up and down adjacent the outer sides of the loader. Generally, the bucket and boom structure is raised and lowered by a hydraulic lift cylinder which is interconnected between the vehicle or a support thereon and the boom structure which is actuated by a control lever in the operator's station.
For certain working situations and for other convenience reasons such as inspection, repair, maintenance, and storage, it is desirable to maintain a bucket and boom structure at a given elevation. Since many of the loaders today employ hydraulics for powering the loader boom, it is desirable to provide a secondary locking mechanism to prevent the boom structure from suddenly lowering due to a loss of hydraulic pressure, a failure in the hydraulic system, or an accidental movement of the control lever.
Loader designs involving conventional secondary locking mechanisms that prevent the boom structure from lowering due to movement of the control lever, i.e., a powered lowering force, present special challenges. That is, the associated loader components must be sufficiently robust to withstand a lowering force that may be applied at maximum hydraulic pressure. Therefore, the extent of the increase of such load carrying capacity typically requires an increase in material thickness and weight of structural components. As a result, the work vehicle purchase price and cost to operate the work vehicle increases.
Accordingly, it would be advantageous for work vehicles to include structurally reliable secondary locking mechanisms for booms without requiring the normally requisite increase in component load carrying capacity and costs associated therewith.